Method of forming metal line of inductor

ABSTRACT

A method of forming a metal line of an inductor used in a Radio Frequency (RF) device, effectively removes polymer generated during an etching process to form trenches. The method removes the polymer using a radical having a high reactivity with the polymer. The method includes carrying out first main etching to form the trenches, carrying out ashing to remove polymer generated in the first main etching, and carrying out second main etching to form vias on the bottoms of the trenches.

The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2008-0080352 (filed on Aug. 18, 2008), which is hereby incorporated by reference in its entirety.

BACKGROUND

This disclosure relates to technique of forming an RF inductor used as an RF passive device in semiconductor devices. In order to reduce resistance of metal in a process of forming the RF inductor, a film height may be increased. A process of etching trenches filled with a metal line for the inductor may be referred to as an Ultra Thick Metal (UTM) etching process. However, in a related method of manufacturing an RF inductor, problems may arise due to the generation of polymer. These problems will be described with reference to FIGS. 1 and 2.

FIG. 1 is a photograph illustrating presence of polymer on sidewalls of trenches, on which UTM Reactive Ion Etching (RIE) is carried out. Trenches formed by UTM RIE have a large line width and a large depth, compared with general trenches.

In the case of a UTM having the above design rule, a large amount of polymer is generated during the UTM RIE. As illustrated in FIG. 1, the polymer is present on the sidewalls of the trenches after the UTM RIE has been carried out. The thickness of the polymer may be substantial, for example, 70 nm or more. The polymer may be formed over the bottoms and the sidewalls of the trenches and a photoresist (PR) of the trenches.

The polymer described above may be generated during the UTM etching process. A large amount of the polymer may also be generated during a process of etching vias using a nitride film as a mask. This large amount of the polymer may be removed through a subsequent ashing process. In the related art, there is a limit to the completeness of the removal of the polymer generated during the UTM RIE using only the ashing process. The main purpose of the ashing process is to remove the PR used in the trench etching process.

FIGS. 2A and 2B are photographs illustrating presence of polymer after the general ashing process. With reference to FIGS. 2A and 2B, after the subsequent ashing process has been carried out, the polymer generated during the UTM RIE remains. The remaining amount of the polymer is lifted off and separated from the trenches, thus causing a fatal defect of a device. Thereby, lifespan and yield of the device are greatly reduced.

In general, the related ashing process is carried out in a high-pressure oxygen (O₂) gas atmosphere. The reactivity of oxygen (O₂) is effective to remove the PR used in the UTM RIE. However, oxygen (O₂) does not remove the polymer generated in the UTM RIE.

Therefore, since the UTM RIE in the related art requires deeper etching, the time required in the etching process is increased. A large amount of polymer is generated due to this increase of the process time. Further, a subsequent process does not effectively remove the polymer generated in the UTM RIE, thus causing a fatal defect of a device.

SUMMARY

Embodiments relate to a semiconductor device, and more particularly, to method of forming a metal line of an inductor used in a Radio Frequency (RF) device. More particularly, embodiments relate to a method of forming a metal line of an inductor, which includes removal of polymer generated in Ultra Thick Metal (UTM) Reactive Ion Etching (RIE). Embodiments relate to a method of forming a metal line of an inductor, which includes removal of polymer generated in formation of trenches by UTM RIE, prior to a subsequent process of forming vias. Embodiments relate to a method of forming a metal line of an inductor, which removes polymer generated in etching for formation of trenches, using a radical having a high reactivity with the polymer.

Embodiments relate to a method of forming a metal line of an inductor which may include carrying out first main etching to form trenches, carrying out ashing to remove polymer generated in the first main etching, and carrying out second main etching to form vias on the bottoms of the trenches. In the first main etching, the trenches may be formed through Reactive Ion Etching (RIE). In the ashing, a nitrogen (N) or fluorine (F) based radical having a high reactivity with the polymer may be used as a process gas. The polymer may be removed from the sidewalls of the trenches. The method may further include carrying out ashing to remove the residue of a photoresist used to form the trenches in the first main etching. The ashing to remove the residue of the photoresist may be carried out in an oxygen (O₂) atmosphere.

Embodiments relate to a method of forming a metal line of an inductor which may include forming an insulating film over a substrate, forming a photoresist pattern to form trenches over the insulating film, forming the trenches on the insulating film through Reactive Ion Etching (RIE) using the photoresist pattern, removing the photoresist pattern, removing polymer in the trenches, and forming vias on the bottoms of the trenches. In the removal of the polymer, ashing using a nitrogen (N) or fluorine (F) based radical as a process gas may be carried out. The method may further include removing the residue of the photoresist pattern, after the removal of the photoresist pattern. The method may further include forming the metal line by filling the trenches and vias with a metal.

DRAWINGS

FIG. 1 is a photograph illustrating presence of polymer on sidewalls of trenches, on which Ultra Thick Metal (UTM) Reactive Ion Etching (RIE) is carried out.

FIGS. 2A and 2B are photographs illustrating presence of polymer after a related ashing process.

Example FIG. 3 is a block diagram schematically illustrating an apparatus used in the UTM RIE and the ashing process.

Example FIG. 4 is a diagram illustrating processes to effectively remove polymer in a method of forming a metal line of an inductor in accordance with embodiments.

Example FIG. 5 is a photograph illustrating line serration due to addition of a de-polymer process in the UTM RIE.

Example FIG. 6 is a photograph illustrating a result obtained by carrying out the de-polymer process for 50 seconds or more.

Example FIG. 7 is a diagram illustrating processes to effectively remove polymer in a method of forming a metal line of an inductor in accordance with embodiments.

DESCRIPTION

Example FIG. 3 is a block diagram schematically illustrating an apparatus used in Ultra Thick Metal (UTM) Reactive Ion Etching (RIE) and an ashing process. The apparatus of example FIG. 3 is an HPT etching apparatus, which may include first and second RF generators 10 and 20 to employ dual frequencies. The HPT etching apparatus may further include a showerhead 30 serving as a gas injection unit, and a turbo pump 40 and a throttle valve 41 to maintain a low vacuum.

To form a plasma potential, the first RF generator 10 generating a frequency of 27 MHz and an upper electrode for the 27 MHz RF energy may be used. To carry out etching through vertical force, the second RF generator 20 generating a frequency of 2 MHz and a lower electrode for the 2 MHz RF energy may be used. Further, to allow fine control of the flow of plasma, a flow confinement ring may be used. In embodiments, the processes described below may be sequentially carried out to effectively remove polymer using the above apparatus.

First, a UTM RIE process to form trenches may be carried out. After, a de-polymer process may be carried out. Thereafter, an etching process to form vias on the bottoms of the trenches may be carried out.

Specifically, example FIG. 4 illustrates processes to effectively remove polymer in a method of forming a metal line of an inductor in accordance with embodiments. To form the metal line, an insulating film may first be formed over a substrate. Here, an oxide film may be used as the insulating film. However, the insulating film is not limited to the oxide film.

Thereafter, a photoresist pattern to form trenches may be formed over the insulating film. A first main etching process (ME1) using the photoresist pattern as a mask may be carried out (S1). In this way, the trenches are formed in the insulating film. In embodiments, the first main etching process (ME1) employs UTM RIE, and may use Ar, CF₄, CHF₃, and O₂ as an etching gas.

Thereafter, a de-polymer process to remove polymer generated in the first main etching process may be carried out (S2). Here, the de-polymer process may be an ashing process, and may use a nitrogen (N) or fluorine (F) based radical, having a high reactivity with the polymer, as a process gas. In particular, the polymer generated at the sidewalls of the trenches may be removed through the de-polymer process.

Further, a process of removing the photoresist pattern used in the formation of the trenches during the first main etching process and an ashing process for removing the residue of the photoresist may be carried out before or after the above de-polymer process. Here, such an ashing process may be carried out in an oxygen (O₂) atmosphere.

After the above ashing processes have been completed, a second main etching process (ME2) to form vias on the bottoms of the trenches may be carried out (S3). The second main etching process (ME2) to form the vias may be a self-aligned hole (SAC) etching process, and may use Ar, CO, C₄F₈, and O₂ as an etching gas.

In embodiments, the de-polymer process to remove the polymer ma not additionally be carried out during the UTM RIE of the first main etching process (ME1), as described above. If the de-polymer process is additionally carried out during the UTM RIE, line serration may become severe due to destruction of the upper part of the film, as shown in example FIG. 5. Further, deformation of the central regions and corner regions of the trenches due to the etching may become severe, and nitride, which is used in the SAC etching process to form the vias, may scarcely remain over the central regions of the trenches.

Based on the above result, if the de-polymer process is additionally carried out during the UTM RIE, the vias may not be sufficiently opened, or a large attack may be applied to the upper surface of a lower metal portion during the subsequent via forming process.

Therefore, in embodiments, as described above, the de-polymer process to remove the polymer may not additionally be carried out during the UTM RIE, but the polymer generated during the UTM RIE may be removed using a gas having a high reactivity with the polymer in the subsequent ashing process. Here, a nitrogen (N) or fluorine (F) based radical having a high reactivity with the polymer may be used to remove the polymer.

The de-polymer process may be carried out for 50 seconds or more, for example. That is, in embodiments, an etching target of the de-polymer process may be split off for 50 seconds or more. Finally, a process of forming the metal line of the inductor may be carried out. To form the metal line, the trenches and the vias may be filled with a metal.

Example FIG. 6 illustrates a result obtained by the de-polymer process carried out for 50 seconds or more. From example FIG. 6, it may be seen that the polymer is completely removed from the insides of the trenches by sufficiently carrying out the de-polymer process.

Although, in embodiments, the de-polymer process to remove the polymer is not additionally carried out during the UTM RIE of the first main etching process (ME1), the polymer may be more effectively removed through improvement of the UTM RIE.

In accordance with embodiments, the UTM RIE to form trenches is improved, other than the de-polymer process to remove the polymer in the trenches, as described above.

Specifically, Ar, CF₄, CHF₃, and O₂ may be used in the UTM RIE in accordance with embodiments. As to etching conditions, as the amount of O₂ gas is increased, a bias power is set to 0 watts, thereby improving removal of the polymer from the sidewalls of the trenches. For example, the UTM RIE may be carried out at a high temperature under the conditions that a bias power is set to 0 watts, the amount of O₂ is 700 sccm, the amount of CF₄ is 7 sccm, and the amount of N₂ is 100 sccm.

In embodiments, an ashing process to remove the polymer is carried out after the UTM RIE has been carried out under the above conditions. Specifically, example FIG. 7 illustrates processes to effectively remove polymer in a method of forming a metal line of an inductor in accordance with embodiments.

In order to form the metal line, an insulating film may first be formed over a substrate to form the metal line, and then trenches may be formed in the insulating film through RIE. A first de-polymer process to remove the polymer generated during the RIE from the sidewalls of the trenches may be carried out (S10). Here, as conditions of the de-polymer process, a high power may be used, a bias power of 0 watts may be applied, and Ar, CF₄, O₂, and N₂ may be used as a process gas.

Thereafter, a second de-polymer process to remove the polymer from the bottoms and tops of the trenches may be carried out (S20). Here, as conditions of the de-polymer process, a high power may be used, a bias power of a uniform level may be applied, and Ar, CF₄, O₂, and N₂ may be used as a process gas. Thereafter, a main ashing process may be carried out after the above de-polymer processes (S30) to remove the residue of a photoresist. The main ashing process is carried out in an oxygen (O₂) atmosphere.

As apparent from the above description, after UTM RIE to form trenches is carried out, polymer in the trenches is effectively removed using a nitrogen (N) or fluorine (F) based radical having a high reactivity with the polymer as a process gas.

Therefore, although a large amount of the polymer may be formed during the UTM RIE requiring a long process time, the polymer generated during the UTM RIE is effectively removed in a subsequent process. Thereby, the lifespan and yield of a device are greatly increased.

It will be obvious and apparent to those skilled in the art that various modifications and variations can be made in the embodiments disclosed. Thus, it is intended that the disclosed embodiments cover the obvious and apparent modifications and variations, provided that they are within the scope of the appended claims and their equivalents. 

1. A method comprising: carrying out a first main etching to form trenches; carrying out ashing to remove polymer generated in the first main etching; and carrying out a second main etching to form vias on the bottoms of the trenches.
 2. The method of claim 1, wherein in the first main etching, the trenches are formed through reactive ion etching.
 3. The method of claim 1, wherein in the ashing, a nitrogen based radical having a high reactivity with the polymer is used as a process gas.
 4. The method of claim 3, wherein the polymer is removed from the sidewalls of the trenches.
 5. The method of claim 1, wherein in the ashing, a fluorine based radical having a high reactivity with the polymer is used as a process gas.
 6. The method of claim 5, wherein the polymer is removed from the sidewalls of the trenches.
 7. The method of claim 1, comprising carrying out ashing to remove the residue of a photoresist used to form the trenches in the first main etching.
 8. The method of claim 7, wherein the ashing to remove the residue of the photoresist is carried out in an oxygen atmosphere.
 9. The method of claim 1, including filling the trenches and vias with metal to form a metal line of an inductor.
 10. A method comprising: forming an insulating film over a substrate; forming a photoresist pattern over the insulating film to form trenches; forming the trenches on the insulating film through reactive ion etching using the photoresist pattern; removing the photoresist pattern; removing polymer in the trenches; and forming vias on the bottoms of the trenches.
 11. The method of claim 10, wherein in the removal of the polymer, ashing using a nitrogen based radical as a process gas is carried out.
 12. The method of claim 10, wherein in the removal of the polymer, ashing using a fluorine based radical as a process gas is carried out.
 13. The method of claim 10, further comprising removing the residue of the photoresist pattern, after the removal of the photoresist pattern.
 14. The method of claim 10, further comprising forming a metal line of an inductor by filling the trenches and vias with a metal.
 15. An apparatus configured to: carry out a first main etching to form trenches; carry out ashing to remove polymer generated in the first main etching; and carry out a second main etching to form vias on the bottoms of the trenches.
 16. The apparatus of claim 15, configured to form the trenches in the first main etching through reactive ion etching.
 17. The apparatus claim 15 configured to use as a process gas, in carrying out the ashing, one of a nitrogen based radical and a fluorine based radical, having a high reactivity with the polymer.
 18. The apparatus of claim 17, wherein the polymer is removed from the sidewalls of the trenches.
 19. The apparatus of claim 15, configured to carry out ashing, in an oxygen atmosphere, to remove the residue of a photoresist used to form the trenches in the first main etching.
 20. The apparatus of claim 15, configured to fill the trenches and vias with metal to form a metal line of an inductor. 